X-rays have long been used to acquire images of the interior of the patient's body for diagnostic purposes. More recently, X-ray equipment has been used for assisting in invasive techniques, such as biopsies and lithotripsy. For example, in X-ray mammography the breast of the patient is X-rayed and X-ray films are used to determine whether there are any micro-calcifications or other growths (hereinafter generally termed "lesions"). If a lesion is discovered then it is necessary to determine if the lesion is benign or if it requires immediate treatment. For such a determination, it is often necessary to perform a biopsy. To assist the surgeon in locating the lesion for the biopsy, the radiologist inserts a radio opaque needle holder adjacent to the growth. A barbed needle is then inserted through the holder into the center of the suspected growth and the needle holder is removed. The point of the needle indicates to the surgeon the exact location of the tissue to be excised.
In greater detail, with the prior art systems, the patient was brought to the mammographic X-ray system. The patient's breast was compressed between horizontal plates attached to the X-ray equipment with a C-arm. The C-arm is a "C" shaped bracket which normally holds the X-ray tube at the top of the "C" and the X-ray beam receptor at the bottom of the "C". The radiologist marked the breast or one of the compression plates at a point in the plane where he thought the lesion was located based on the study of a preliminary X-ray. A new X-ray image was then taken and developed to determine whether the marking was indeed in the correct location. If the marking was not in the correct location, then the radiologist repeated the marking procedure and acquired another X-ray image. When the marking was indeed aligned with the lesion, then the radiologist inserted the needle holder into the compressed breast through an aperture or recess in the compression plate at the marked point so as to center the needle tip within the lesion.
The breast was then removed from compression plate and the C-arm was rotated 90.degree.. The breast was again compressed but now with the compression plates vertically aligned. Still another X-ray was acquired to check the alignment of the needle holder tip and lesion in the vertical plane to assure that the holder tip was in the proper location. If the holder tip was not within the lesion the needle holder was moved and another image was acquired. The process was repeated until coincidence between views was obtained.
Then the needle was inserted into the holder and the holder was withdrawn leaving the needle pointing out the exact location of the lesion for the surgeon.
Thus, in prior art X-ray mammography a multiplicity of X-ray images and a plurality of breast clamping operations were required to position the needle to locate the lesion for the surgeon. The repeated operations besides being time-consuming and uncomfortable for the patient, also subjected the patient to the relatively substantial X-ray dosage required to acquire the many images.
Radiologists and scientists were and are seeking to improve the biopsy needle positioning procedure. For example, in March, 1984, a presentation at the National Conference on Breast Cancer of the American College of Radiation described a technique for mammographic needle localisation of lesions which cannot be imaged in two orthoginal views, but only in one of them. In the described technique, the X-ray beam is moved 30.degree. in a xeromammographic system where there is no breast clamping. An article describing the presentation appeared in "The American Journal of Radiology", Vol. 144, pp. 911-916, in May of 1985. The article describes a method that does not use C-arm clamping whereby it is possible to locate the needle using images taken at two positions, 30.degree. apart.
In the past mammographic compression devices for X-ray film mammographic systems used what may be described as "dependent compression". At the top of the C-arm, there was an X-ray tube and collimator arrangement which served as the source of the X-ray beam. A cone extended from the source to the breast to compress the breast against the X-ray radiation receptor or film at the bottom of the C-arm. A removable X-ray film container was provided at the other side of the compression means.
Rotating the C-arm also rotated the compression means. Subsequently, movable compression plates were attached to the C-arm between the X-ray source at the top of the C-arm and the X-ray receptor (i.e. the film) at the other end. The movable compression plates were removably attached along the longitudinal axis of the C-arm to adjust to the woman's breast. In this arrangement, the compression plates rotate with the C-arm. Thus, this arrangement also required unclamping and reclamping the breast when the C-arm was rotated even through small angles.
Compression plates are important in mammography. They improve the quality of the image and thereby enable the discovery of more lesions. When the breast is compressed, it flattens and absorbs less X-ray beams and it absorbs the X-ray beams more uniformly. In addition, extraneous movements are eliminated. These beneficial results of clamping improve the quality of the image. Therefore, it is highly desirable to compress the breast for mammograph breast image processing.
From the above description of the prior art, it is readily understood that it would save time and reduce patient discomfort if a system could be provided that generates an immediate image to aid in positioning the lesion-locating needle holder for biopsy purposes. It would save further time and discomfort if it could utilize a single clamping position and avoid movements of the lesion during reclamping with the consequent relative movement of needle holder and lesion.
These functions are provided in the system described in U.S. Pat. No. 4,821,727 which issued on Apr. 18, 1989, and is assigned to the Assignee of this Patent Application. That Patent describes a system using an imaging chain rather than film for determining the location of the needle holder and also uses a clamping means that does not require reclamping of the breast when the source of the X-rays is moved to obtain another perspective view needed to absolutely locate the needle holder in the interior of the breast. The system described herein improves on the patented system in that, among other things, it provides for obtaining the image of the needle holder in less time than was required with the patented system.
Thus, an object of the system described herein is to position the biopsy needle in a minimum of time with a minimum of X-ray dosage and maximum of accuracy.